Skeleton member structures having skeleton or structural members filled with filling materials are know from, for example, (1) paper pre-published for 2001 JSAE (Society of Automotive Engineers of Japan) Spring General Meeting, entitled “ATTEMPT TO COPE WITH BOTH CRASHWORTHINESS AND WEIGHT REDUCTION” (hereinafter called Prior Art 1), (2) science paper, 1986, The university of Manchester, England, “STATIC AND DYNAMIC AXIAL CRUSHING OF FOAM-FILLED SHEET METAL TUBES” (hereinafter called Prior Art 2), (3) paper published in Automobile Engineering, Vol. 55, April, 2001, “DEVELOPMENT OF A METHOD OF ENHANCING BODY FRAME STRENGTH USING STRUCTURAL FOAM” (hereinafter called Prior Art 3), (4) Japanese Patent Laid-Open Publication No. 2001-130444 entitled “IMPACT ENERGY ABSORBING MEMBER” (hereinafter called Prior Art 4), and (5) Japanese Patent Laid-Open Publication No. 2000-46106 entitled “DAMPING PANEL” (hereinafter called Prior Art 5).
Methods for forming solidified granular materials are know from, for example, (6) U.S. Pat. No. 4,610,836 entitled “METHOD OF REINFORCING A STRUCTURAL MEMBER” (hereinafter called Prior Art 6), (7) the art for solidifying a granular material by use of a resin material (hereinafter called Prior Art 7), (8) the art for solidifying a granular material by a crosslinking liquid film (hereinafter called Prior Art 8), and (9) the art for solidifying a granular material in itself (hereinafter called Prior Art 9).
Prior Art 1 is directed to the art of filling the skeleton member of an automobile with a foamed filling material to realize weight reduction while ensuring absorption energy during a collision.
In Prior Art 2, FIG. 3(b) (ii) at pp. 301 shows an example in which a tube of square cross section filled with polyurethane foam is deformed.
Prior Art 3 discloses the art of filling a part of the interior of a frame with a foamed resin to restrain local buckling deformation of the frame by dispersing the energy of a collision.
(4) Prior Art 4 describes in paragraph [0025] at page 4 that “in order that the impact energy absorbing member can easily receive an impact load in the surface direction thereof, in the case where the impact energy absorbing member has a cavity portion, it is preferable that fitting matter such as grains, a foamed material or a core be fitted into the interior of the impact energy absorbing member to enhance the longitudinal rigidity of the impact energy absorbing member”. In addition, FIG. 14 of the same publication discloses an impact energy absorbing member having an interior in which fitting matter is fitted.
(a) and (b) of FIG. 1 of Prior Art 5 illustrate a damping panel which is filled with a mixture of high rigidity grains and low elastic grains for absorbing vibration energy according to elastic deformation.
FIG. 2 of Prior Art 6 illustrates a structure in which a skeleton member is filled with adhesive-coated glass microspheres wrapped in cloth made of glass fiber. U.S. Pat. No. 4,695,343 also discloses a similar structure.
Prior Art 7 will be described below with reference to FIGS. 27 and 28 hereof.
FIG. 27 shows a structural member 402 in which a skeleton member 400 which constitutes a skeleton structure is filled with a solidified granular material 401.
The solidified granular material 401 shown in FIG. 28 is made of granular materials 403 and a resin material 404 with which the spaces among the granular materials 403 are filled to solidify the granular materials 403.
Prior Art 8 will be described below with reference to FIG. 29 hereof.
The solidified granular material 410 shown in FIG. 29 has a structure in which adjacent ones of the granular materials 403 are bonded to one another by a crosslinking liquid film 411. In the formation of this bonding structure, after moisture or the like has been added to the granular materials 403, the granular materials 403 are pressed and heated to form the crosslinking liquid film 411, thereby forming the solidified granular material 410.
The solidified granular material 420 shown in FIG. 30 is matter in which adjacent ones of the granular materials 403 are bonded to one another by melting the surfaces of the granular materials 403. Reference numeral 421 denotes a solidified portion in which the surfaces of the granular materials 403 are solidified after having been melted.
Prior Arts 1 to 3 have a structure in which a skeleton member is filled with a foamed material, but has the following problem. This problem will be described below with reference to the graphs shown in FIGS. 20A and 20B.
FIG. 20A is a graph for explaining the relationship between the foaming ratio of a foamed material and the buckling load at which buckling occurs when a compressive load is applied to a structural member in the axial direction thereof, and the vertical axis represents the buckling load and the horizontal axis represents the foaming ratio. According to this graph, when the buckling load of the structural member is to be increased, it is necessary to reduce the foaming ratio.
FIG. 20B is a graph for explaining the relationship between the foaming ratio of the foamed material and the weight of the structural member, and the vertical and horizontal axes represent the weight and the foaming ratio, respectively. According to this graph, as the foaming ratio is made smaller, the weight of the structural member increases.
It can be seen from these graphs that in the range of foaming ratios not higher than a foaming ratio at which a predetermined buckling load b is ensured (in the foamed-material effective area shown in FIG. 20B), the weight becomes large and a reduction in the weight of the structural member becomes difficult.
Crush tests of structural members which are respectively filled with the foamed materials disclosed in the aforementioned Prior Arts 1 to 3 and the grains disclosed in Prior Art 4, for example, solid powder will be described below with reference to FIGS. 21A, 21B and 21C.
In FIG. 21A, an axial compressive load P as shown by an arrow is applied to a structural member 300 having a tubular skeleton member 300a filled with a foamed material or solid grains, thereby forcedly deforming the structural member 300.
In FIG. 21B, letting λ be the amount of deformation of the structural member 300, and as the amount of deformation λ increases, the structural member 300 is buckled and deformed into the Z-shaped or dogleg-shaped configuration shown in FIG. 21B.
FIG. 21C is a graph for explaining the relationship between the amount of deformation λ and the load P with the structural member 300 deformed as described above, and the vertical and horizontal axes represent the load P and the amount of deformation λ, respectively. In addition, three kinds of samples are used: a sample A which has an interior not filled with a filling material and uses only a skeleton member, a sample B filled with a foamed material, and a sample C filled with solid grains.
When the amount of deformation λ is small, the sample B (filled with a foamed material) generates a larger load than the sample A, and as the amount of deformation λ becomes larger, the load P sharply decreases.
Regarding the sample C (filled with solid grains), as the amount of deformation λ becomes comparatively larger, the load P sharply decreases. This is because in each of the samples B and C, since the foamed material or the solid grains are not easily crushed in an early stage of deformation, the internal pressure of the structural member excessively rises and is buckled into a Z-shaped or dogleg-shaped configuration and the load P is sharply decreased by this buckling.
Then, a crush test of the structural member of Prior Art 5 that is filled with high rigidity grains and low elastic grains will be described below with reference to FIGS. 22A, 22B and 22C.
In FIG. 22A, the structural member 301 is a member in which a tubular skeleton member 301a is filled with a multiplicity of low elastic grains 302 and a multiplicity of high rigidity grains 303. First, the load P which is an axial compressive load is applied to the structural member 301, thereby forcedly deforming the structural member 301. As a result, the low elastic grains 302 are gradually deformed as shown in FIG. 22B. When the amount of deformation λ of the structural member 301 reaches L, the low elastic grains 302 are nearly completely crushed, and then the load P directly acts on the high rigidity grains 303.
FIG. 22C is a graph for explaining the relationship between the amount of deformation λ of the structural member and the load P when the structural member 301 is deformed as described above, and the vertical and horizontal axes represent the load P and the amount of deformation λ, respectively. In addition, the sample A shown by a solid line includes only the skeleton member shown in FIG. 21C, and a sample D shown by a dashed line is the structural member 301 described with reference to FIGS. 22A and 22B.
The load P of the sample D is nearly equal to that of the sample A until the amount of deformation λ reaches L, but when the amount of deformation λ exceeds L, the load P sharply increases. This is because, as described above, when the amount of deformation λ exceeds L, the load P acts on the high rigidity grains which are hardly crushed, and the load P sharply increases. When the load P is made to act further, the sample D is buckled and deformed into a Z- or doglegged-shape similar to that shown in FIG. 21B, and the load P sharply decreases.
Then, a bending test of a structural member filled with a filling material will be described with reference to FIGS. 23A to 23F.
FIG. 23A shows the state in which a structural member 300B having the skeleton member 300a filled with a foamed material (the sample B shown in FIG. 21C) is supported at two supporting points 306, 306. δ denotes the amount of deformation of the structural member 300B to which a load is applied (the definition of δ is the same in the following description).
FIG. 23B shows the fact that the skeleton member 300a of the structural member 300B is filled with a foamed material 308.
In FIG. 23C, when a load W is applied to the structural member 300B in a direction perpendicular to the axis of a structural part 3200B, i.e., in the direction of an arrow, the structural member 300B is bent downwardly.
As shown in FIG. 23D, the granular materials 308 between a top side 311 and a bottom side 312 of the skeleton member 300a are compressed and lateral sides 313 and 314 of the structural member 300a are swollen outwardly, whereby the lateral sides 313 and 314 peel off the foamed material 308.
As shown in FIG. 23E, when the load W is further applied to the structural member 300B, the structural member 300B is further deformed, and as shown in FIG. 23F, the structural member 300B is crushed to a further extent in the vertical direction, and the lateral sides 313 and 314 are swollen sideways to a further extent.
As shown in FIGS. 23D and 23F, as deformation proceeds, the lateral sides 313 and 314 of the skeleton member 300a peel off the foamed material 308, so that the foamed material 308 becomes unable to easily restrain the deformation of the structural member 300B.
Then, a bending test of a skeleton member filled with solid grains will be described with reference to FIGS. 24A to 24F.
FIG. 24A shows the state in which a structural member 300C having the skeleton member 300a filled with solid grains (the sample C shown in FIG. 21C) is supported at two supporting points 306, 306.
FIG. 24B shows the fact that the structural member 300a is filled with solid grains 317.
As shown in FIG. 24C, when the load W is applied to the structural member 300C in a direction perpendicular to the axis of the structural member 300C, i.e., in the direction of a white arrow, the structural member 300C is bent downwardly. As shown in FIG. 24D, the solid grains 317 between the top side 311 and the bottom side 312 of the structural member 300a are compressed and the lateral sides 313 and 314 of the skeleton member 300a are swollen outwardly, whereby the solid grains 317 spread sideways according to the swelling of the lateral sides 313 and 314.
As shown in FIG. 24E, when the load W is further applied to the structural member 300C, the structural member 300C is further deformed and the bottom side of the structural member 300C is broken. Namely, as shown in FIG. 24F, the structural member 300C is crushed to a further extent in the vertical direction and the lateral sides 313 and 314 are swollen sideways to a further extent, so that the internal pressure becomes excessively large and the bottom side 312 is broken.
Accordingly, when the skeleton member 300a is broken, the flexural rigidity of the structural member 300C becomes extremely low.
FIGS. 24A to 25F show a bending test of a structural member having a skeleton member filled with low elastic grains and high rigidity grains.
FIG. 25A shows the state in which the structural member 301 the skeleton member 301a filled with low elastic grains and high rigidity grains (the sample D shown in FIG. 22C) is supported at the two supporting points 306, 306.
FIG. 25B shows the fact that the skeleton member 301a is filled with the low elastic grains 302 and the high rigidity grains 303.
As shown in FIG. 25C, when the load W is applied to the structural member 301 in a direction perpendicular to the axis of the structural member 301, i.e., in the direction of an arrow, the structural member 301 is bent downwardly, and as shown in FIG. 25D, the load acts on the low elastic grains 302 and the high rigidity grains 303 between the top side 311 and the bottom side 312 of the skeleton member 301a, and the low elastic grains 302 are shrunk and the lateral sides 313 and 314 of the skeleton member 301a are swollen outwardly, whereby the low elastic grains 302 and the high rigidity grains 303 spread sideways according to the swelling of the lateral sides 313 and 314.
As shown in FIG. 25E, when the load W is further applied to the structural member 301, the structural member 301 is further deformed and the bottom side of the structural member 301 is broken. Namely, as shown in FIG. 25F, the structural member 301 is crushed to a further extent in the vertical direction and the lateral sides 313 and 314 are swollen sideways to a further extent, so that the internal pressure becomes excessively large and the bottom side 312 is broken.
Accordingly, when the skeleton member 301a is broken, the flexural rigidity of the structural member 301 becomes extremely low.
The results of the conventional structural members filled with the respective filling materials are shown in the graph of FIG. 26. FIG. 26 shows the results of the sample A and the samples B to D shown in FIGS. 23 to 25. The vertical axis represents the load W applied to the structural member, while the horizontal axis represents the amount of deformation δ.
The load W of the sample B is generally large with respect to that of the sample A, but as the amount of deformation δ increases, the load W gradually decreases.
In the case of the sample C and the sample D, the value of the load W increases in an early stage of deformation, but since the load W sharply decreases while the amount of deformation δ is small, the maximum amount of deformation δ is small.
Absorption energy capable of being absorbed by a structural member during a vehicle collision is nearly equivalent to the result obtained by, letting δ be a small amount of deformation, integrating the load W corresponding to this small amount of deformation from zero to maximum in terms of the amount of deformation δ, i.e., the area below each of the curves. Accordingly, if the load W for each value of the amount of deformation δ can be maintained at a large value and the maximum amount of deformation δ can be increased, the absorption energy of the structural member during the collision can be made large. In addition, if the load W can be made constant, impact energy can be stable absorbed.
In the case of the above-described sample B, the maximum amount of deformation δ is large, but the load W for each value of the amount of deformation δ is not sufficiently large, whereas in the case the samples C and D, the maximum load W is large, but the maximum amount of deformation δ is small. Accordingly, any of the samples B to D is small in total absorption energy, i.e., cannot sufficiently absorbe impact energy.
In the case of the sample C and the sample D, the variation of the load W is large, so that the absorption of impact energy does not stabilize.
In the structure disclosed in Prior Art 6, since individual microspheres are bonded together by an adhesive, solid matter having high rigidity in whole can be formed. However, for example when an impact acts on a skeleton member, if the deformation of each of the microspheres is small, load occurring in the skeleton member sharply increases, so that impact energy cannot be sufficiently absorbed.
In Prior Art 7, as shown in FIGS. 27 and 28, since the granular materials 403 are solidified by the resin material 404, the rigidity of the structural member 402 increases, but the amount of the resin material 404 becomes large to increase the weight of the structural member 402.
In Prior Art 8, as shown in FIG. 29, the mutual bonding of the granular materials 403 by the crosslinking liquid film 411 is based on surface tension, so that bonding force is weak and a large solidified granular material is difficult to form as the solidified granular material 410.
In Prior Art 9, as shown in FIG. 30, the granular materials 403 are solidified by melting the surfaces of the granular materials 403 themselves, so that adjacent ones of the granular materials 403 can be firmly bonded to one another. However, in the case where the granular materials 403 are ceramics, for example, glass, silicon dioxide (SiO2) and aluminum oxide (Al2O3: alumina), the granular materials 403 must be heated at a very high temperature. In addition, since special equipment is needed, it is not easy to form the solidified granular material 420.
Accordingly, there is a demand for a skeleton member structure capable of stable absorbing more impact energy in spite of an restrained increase in weight.